a) Field of the Invention
The present invention relates to an objective lens used for recording to and reproducing from optical recording disks such as CDs and DVDs and a manufacturing method thereof. More specifically, the present invention relates, in an objective lens driving system, to a technology in which driving coils of a magnetic driving circuit for correcting focusing errors and tracking errors of the objective lens are prevented from becoming detached.
b) Description of the Related Art
An optical pickup apparatus used for recording to and reproducing from optical recording disks such as CDs and DVDs employs an objective lens driving system that drives a lens holder retaining an objective lens in focusing and tracking error correcting directions on the holder supporting member by a magnetic driving circuit. In the magnetic driving circuit, permanent magnets are bonded on either the lens holder or holder supporting member, and driving coils are fixed by adhesive on the other member to face the permanent magnets. The driving coil is a flat coil made of a wound self-welding wire in which a heat welding layer is coated around a metallic wire. The self-welding wire is wound and then heated to melt the heat welding layer. With normal temperature, the wound self-welding wire is united with one another. Note that wiring of the driving coil is carried out such that the heat welding layer around the self-welding wire is melted with the heat for soldering to expose the metallic wire, and then the metallic wire is connected electrically. Therefore, a lower melting temperature for the heat welding layer facilitates soldering operation. Conventional technologies have used a self-welding wire whose melting temperature for the heat welding layer is about 140.degree. C.
On the other hand, since the driving coil obtains heat at electrification, the heat welding layer of the self-welding wire is melted with such a heat. Therefore, there is a need to set the melting temperature of the heat welding layer high so that the self-welding wire will not be loosened and detach. Thus, two contradictory needs exist: a need for setting the melting temperature for the heat welding layer high against the heat by electrification of the driving coil, and a need for setting the same low to facilitate soldering operation. Conventionally, the facilitation of soldering has been considered more important, so the melting temperature of the heat welding layer is set low. With this, no problems occur while a normal degree current is applied to the driving coil; however, when an excessive current is applied to the driving coil, the heat welding layer will be melted, and thus the self-welding wire is loosened to detach.